Picking Up the Pace (with VTOL)

By Andrew Drwiega

Andrew Drwiega

Good news on the Science and Technology (S&T) front in terms of pushing forward the performance envelope for vertical takeoff and landing combined with speed and range. The U.S. Defense Research Advanced Projects Agency (DARPA) announced in mid-March that Boeing and Karem Aircraft will now join Sikorsky and Aurora Flight Sciences in the Phase 1 of DARPA’s VTOL Experimental Plane (X-Plane) project.

VTOL X-Plane is seeking to find a hybrid aircraft design that can achieve much more performance and range than the standard helicopter design. The requirements that DARPA is looking for are speed (achieve a top sustained flight speed of 300-400 knots); hover efficiency (raise hover efficiency from 60 percent to at least 75 percent); cruise efficiency (present a more favorable cruise lift-to-drag ratio of at least 10, up from 5-6); and useful load capacity (maintain the ability to perform useful work by carrying a useful load of at least 40 percent of the vehicle’s projected gross weight of 10,000-12,000 lbs).

According to program manager Ashish Bagai, the Phase 1 awards to the four selected companies are for the preliminary concept design and technology maturation. According to the current schedule, the companies will submit their designs by late 2015. At this point DARPA will select one design to take forward to Phase II (design, development and integration) then on to Phase III, which will be an initial flight test around 2017-18.

Bagai said the designs proposed from all four companies were focused on unmanned vehicles, but he adds that the technologies that DARPA is looking for in regard of the X-Plane could also apply to manned vehicles.

The four designs received were: Boeing’s Phantom Swift; Aurora’s Lightening Strike; an unnamed design from Sikorsky Innovations teamed with Lockheed Martin’s Skunk Works; and an unnamed design from Karem Aircraft.

Dan Newman, Boeing Phantom Works Advanced Vertical Lift capture team lead, said that the challenge of providing all of DARPA’s requirements “in a single aircraft has been the holy grail for tactical military aviation.”

He continued: “Designing an aircraft to perform a vertical takeoff, while maintaining adequate low-speed control, is challenging. Sustaining efficient hover is also difficult, and adding a high cruising speed is even more challenging.”

Chris Van Buiten, vice president of Sikorsky Innovations, said that the X-Plane program “explores a generation of innovation that has yet to be introduced.” Mark Miller, Sikorsky’s vice president of research and engineering, added that the Sikorsky/Lockheed Martin proposal was based on a “non-traditional technical solution.”

According to Sikorsky, a scaled down version of its Phantom Swift flew last year. The aircraft features two large lift fans within the fuselage which are covered when the aircraft is in cruise mode. Wingtip-mounted ducted fans will provide the forward thrust and additional hover lift.

Aurora’s LightningStrike will incorporate aspects of the company’s VTOL technology. The company has worked with DARPA for well over a decade on projects including GoldenEye 100, GoldenEye 80 and the Excalibur UAV proof-of-concept for the US Army between 2005 and 2010. The latter combined hybrid-electric propulsion for VTOL and high-speed horizontal flight.

There seem to be slightly different financial awards from company to company. Boeing says it has a “$17 million agreement with DARPA’s Tactical Technology Office,” while Sikorsky states that “the proposed effort is valued at $15 million to develop the preliminary design.”

While there is no official statement linking this program to the U.S Army’s Future Vertical Lift (Heavy) requirement, it should be noted that Sikorsky, Boeing and Karem are all participants in the Joint Multi-Role program which will eventually lead to the Future Vertical Lift (Medium) aircraft, which will replace the Army’s medium helicopter fleets of AH-64 Apaches and UH-60 Black Hawks.

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